Project Summary The medial temporal lobe (MTL) plays a critical role in the rapid formation of episodic memories in human and nonhuman primates, while research performed in freely-moving rodents has likewise identified these same structure as being pivotal for spatial navigation. Each of these lines of work reflect powerful research traditions that have significantly contributed to our understanding of medial temporal lobe function, but questions remain about how to reconcile their considerable data sets. One compelling hypothesis is that the same neural mechanisms that support the role of MTL in spatial navigation also support the formation of episodic memories. We propose an innovative set of experiments designed to directly test this hypothesis Our approach involves recording neural activity from the same neurons in the medial temporal lobe of marmoset monkeys in two contexts. One involves head-restrained subjects performing a recognition memory task typical of human experiments while in the other freely-moving subjects navigate spatial environments commonly used in studies of rodents. Our innovative approach will allow us to test ? for the first time - whether the same neurons in primate medial temporal lobe support behaviors performed in tasks representative of these two research traditions. Aim 1 seeks to characterize recognition memory in marmosets using a task that ? like spatial navigation ? relies on incidental memory formation. Experiments in Aim 2 examine the role of the hippocampal CA fields and entorhinal cortex in spatial navigation, including the putative existence of place cells and grid cells, respectively. Aim 3 directly tests the principal question of this proposal by recording from the identical neurons while subjects perform the recognition memory task in Aim 1 and navigate spatial environments similar to studies in Aim 2.